JPH09331669A - Drive circuit for voltage drive type semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reliability by surely protecting a voltage drive type semiconductor element from an overcurrect generated by a short-circuit accident or the like thereof. SOLUTION: After turning on an IGBT(Insulated Gate Bipolar Transistor) 4 as a voltage drive type semiconductor element through a one shot circuit 101, a variable voltage source 103 is actuated for only a specified period of time while gradually decreasing its gate voltage, overcurrect trouble is discriminated by a detection circuit 100. At trouble time, through a timer circuit 102 the variable voltage source 103 is operated and the gate voltage is continuously decreased, and at normal time operation of the variable voltage source 103 is stopped. By returning the gate voltage to a regular value, the semiconductor element can be surely protected from element destruction or the like.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an insulated gate bipolar transistor (hereinafter abbreviated as IGBT).
Drive circuit of voltage drive type semiconductor element such as MOS FET and MOS type FET, especially drive circuit of voltage drive type semiconductor element having a function of protecting the semiconductor element from an overcurrent generated at the time of a short circuit accident in a power converter such as an inverter Regarding

[0002]

2. Description of the Related Art In the following description, the case where an IGBT is used as a voltage-driven semiconductor element will be described. In a power converter, a short-circuit accident is a failure that leads to element destruction among overcurrent failures during operation. That is, when a short circuit accident occurs, a short circuit current of about 10 times the DC rating flows through the IGBT element. Therefore, if this short-circuit current is cut off by a normal turn-off operation, when the current is cut off,
As shown by the broken line in FIG. 7A, the collector of the IGBT
The jump voltage V _CEP of the emitter-to-emitter voltage V _CE becomes excessive, and this voltage V _CEP becomes higher than the breakdown voltage of the device, which may lead to device breakdown. As such an overcurrent protection method, the applicant has previously proposed a circuit as shown in FIG. This is to gradually reduce the gate-emitter voltage V _GE of the IGBT at a constant time constant as shown by the solid line waveform in FIG. 7C at the time of a short circuit accident. By doing so, the collector current Ic Figure 7 (b)
It decreases as can reduce the jumping voltage V _CEP voltage V _CE at the time of current interruption.

A more specific description will be given with reference to FIG.
Reference numeral 4 in the figure is an IGBT as a main switching element,
Reference numeral 5 is a signal insulating photocoupler, 6 and 7 are a voltage source for applying an on-gate voltage (V1), and an off-gate voltage (V
2) Indicates a voltage source for application. Here, the normal operation will be described. When the photo coupler 5 turns on, the transistor 8
Is off, the transistor 9 is on, and the transistor 10 is off, so that the on-gate voltage V1 is applied between the gate and the emitter of the IGBT 4 through the resistor 11. When the on-gate voltage is applied, the IGBT 4 turns on, and its collector-emitter voltage drops to the on-voltage (referred to as V _{CE (ON))} . Therefore, V _{ZD (13)} + V _{BE (14)} > V2 + V _{CE (ON)} + VF ₍₁₅₎ V _{ZD (13)} : Zener diode 13 threshold voltage V _{BE (14)} : Transistor 14 base-emitter voltage (V _BE ) VF ₍₁₅₎ : By selecting components in advance so that the forward voltage relationship of the diode 15 is established, the transistor 14 can be turned off when the IGBT 4 is on.

Next, when the photocoupler 5 is turned off, the transistor 8 is turned on, the transistor 9 is turned off, the transistor 10 is turned on, and the off-gate voltage V2 is applied between the gate and the emitter of the IGBT 4 via the resistor 11. Then, the IGBT 4 is turned off. Now, if a short circuit accident occurs during the ON period of the IGBT4, V _{ZD (13)} + V _{BE (14)} <V2 + V _{CE (ON)} + VF ₍₁₅₎ due to the increase in the collector-emitter voltage. , The transistor 14 becomes conductive. As a result, the electric charge of the capacitor 20 is discharged through the resistor 18 (R2). At this time, by selecting R1 and R2 ≧ R3 in advance, the voltage difference between the voltage across the capacitor 20 and V2 will be I through the diode 21 and the transistor 10.
It is applied between the gate and the emitter of the GBT 4. This voltage gradually decreases over time. Since the short-circuit current flowing through the IGBT 4 depends on the voltage applied between the gate and the emitter, the short-circuit current also decreases corresponding to the decrease in the gate-emitter voltage. Therefore, the reduction rate (-di / dt) of the current when shutting off the overcurrent can be suppressed to a small value.

[0005]

In a short circuit accident of the IGBT inverter, there is an inductance Ls in the short circuit path, and the short circuit current may be suppressed by the inductance Ls. FIG. 9A shows a short circuit when there is an inductance Ls, and FIG. 9B shows its operation waveform. That is, when the IGBT is turned on, a short-circuit phenomenon occurs, and the collector current Ic of the IGBT increases by a current increase rate (di / dt = distance) determined by the power supply voltage Ed and the inductance Ls.
Ed / Ls · t), and the increase stops at the maximum current value that the IGBT element can flow (see t = t1 in FIG. 9B). Next, when the collector current Ic reaches a constant value (Icp), the collector-emitter voltage V _{CE of} the IGBT increases, and its value becomes the power supply voltage Ed + ΔV due to the energy stored in the inductance Ls (see FIG. ) T = t1 or later). However, ΔV is the snubber capacitor 7
When the capacity of 03 is C1, ΔV = √ (Ls / C1) · Icp.

In the above-mentioned short-circuit accident, there is a problem that the conventional short-circuit protection system does not work effectively as described below, leading to element destruction. (1) In the conventional short-circuit protection method, since the overcurrent is detected by the voltage value of V _CE , the collector current I
After c reaches the maximum current value (see t = t2 in FIG. 9B), the protection function operates. When the collector current Ic is attenuated by the protection action, the attenuated current flows into the snubber circuit 700 of FIG. 9A, and the snubber voltage increases. Since the snubber voltage is equal to V _CE, V _CE at t = t2 point shown in FIG. 9 (b) is overcharged or the power supply voltage Ed, is further charged by the protective action, are device destruction beyond the breakdown voltage There is a possibility. (2) The capacitance C1 of the snubber capacitor 703 may be increased in order to prevent the element breakdown due to the above-mentioned overcharge, but if this is done, the snubber circuit becomes large and the cost increases. (3) The normal off signal is input during the period when the V _CE voltage value does not reach the overcurrent detection level (before t = t1 in FIG. 9B),
When a large current (usually overcurrent level or higher) is normally cut off, there is a possibility that the device may be destroyed due to deviation from the so-called safe operating area (ASO) of the device. Therefore, an object of the present invention is to surely protect an element from an overcurrent caused by a short circuit accident of a voltage-driven semiconductor element.

[0007]

In order to solve such a problem, according to the present invention, a protection operation for reducing the gate voltage is performed after the turn-on of the IGBT, and after a certain period of time, it is judged whether or not there is a failure, and it is judged as a failure. When it is normal, the protection operation is continued, and when it is judged to be normal, the protection operation is stopped,
It is designed to restore the normal gate voltage value. That is,
The current that can flow in the short-circuited IGBT element is determined by the output characteristics shown in FIG. The output characteristic is divided into a saturated region and an active region, and a short circuit state becomes the active region. As shown in the figure, this active region is a region in which the collector current Ic changes greatly even if the collector-emitter voltage is changed, but the collector current Ic changes greatly due to the change in the gate voltage value V _GE .

Therefore, after the IGBT is turned on, the protection operation is activated to reduce the gate voltage. When the IGBT is in the short-circuited state, the gate voltage value is lower than the regular voltage value, so that the short-circuit current flowing through the element is suppressed to a low current value without being increased to the maximum voltage value determined by the regular gate voltage value. When the increase in short-circuit current stops, the collector-emitter voltage increases and the IGBT enters the active region. That is, if the gate voltage value is reduced, it is possible to forcibly enter the active region at a low short circuit current value. In this state, if the failure is determined and the protection operation is continued, the short-circuit current value can be suppressed and the overcurrent protection function can be effectively used. IG
If the BT is not in a short-circuited state, the collector-emitter voltage does not increase even if the gate voltage is decreased. Therefore, if the failure is identified, the protection operation is stopped, and the gate voltage is returned to the normal voltage value, the normal operation is performed. become.

[0009]

1 is a block diagram showing a first embodiment of the present invention. As is clear from comparison with FIG. 8, in this example, the variable voltage source 103 and the failure detection circuit 100 that monitors the element voltage to detect a failure are separated, and in the meantime, the off signal of the transistor 10 changes the voltage for a certain period. A feature is that a one-shot circuit 101 for operating the voltage source 103 and a timer circuit 102 for delaying an output signal of the failure detection circuit 100 for monitoring a device voltage to detect a failure for a certain period are added.

The operation of FIG. 1 will be described with reference to FIG. First, the turn-on operation will be described. Now, when the photocoupler 5 is turned on, the transistor 8 is turned off (see t = t0 in FIG. 2). As a result, the transistor 9 is turned on, the transistor 10 is turned off, the on-gate voltage V1 is applied between the gate and emitter of the IGBT 4 via the resistor 11, and the IGBT 4 is turned on. IGB
In T4, at the time of t = t1 after turn-on, the one-shot circuit 101 operates by turning off the transistor 10,
The transistor 14 of the variable voltage source 103 is operated. When the transistor 14 is turned on, the electric charge of the capacitor 20 is discharged through the resistor 18 (R2), and the voltage difference between the voltage across the capacitor 20 and V2 is passed through the diode 21 and the transistor 10 and the gate-emitter of the IGBT 4 is discharged. Applied between. That is, the gate voltage V _{GE of the} IGBT 4 will gradually decrease with the passage of time. This decrease in gate voltage V _GE continues until time t = t2.

When the OFF signal of the transistor 10 is input, the timer circuit 102 provided on the output side of the failure detection circuit 100 for monitoring the element voltage and detecting the failure operates, and t = after the timer time. Failure determination is performed at time t2. The relational expression for failure determination is as follows. Normal: V _{ZD (50)} + V _{BE (52)} > V2 + V _{CE (ON)} + V _{F (15)} ... Abnormal: V _{ZD (50)} + V _{BE (52)} <V2 + V _{CE (ON)} + V _{F (15)} ... And At t = t2, if the failure determination result is normal (when the relationship of the above equation is satisfied), the reduction of the gate voltage V _GE is stopped and the normal gate voltage value V1 is restored. The collector-emitter voltage V _CE of the IGBT 4 and the collector current Ic waveform in this case are shown in FIG.

On the other hand, the failure determination result is abnormal (failure:
In the case of satisfying the relationship of the above formula), the gate voltage V
Continue to lower _GE . FIG. 2F shows the collector-emitter voltage V _CE of the IGBT 4 and the collector current Ic waveform in this case. As shown in FIG. 2D, time t =
Since the gate voltage V _GE also decreases after t2, the collector current Ic is suppressed as shown in FIG. I
When the collector current stops flowing in GBT4, the collector-
The voltage between the emitters increases. That is, a current value lower than the maximum current value of the element (when the normal gate voltage value V _GE = V1 is applied) enters the active region. By determining the failure at time t = t2 and continuing the decrease of the gate voltage V _GE , the IGBT 4 can be safely turned off.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention. As is apparent from the figure, the difference from FIG. 1 is that variable voltage sources 70 and 80 having different time constants for lowering the gate voltage V _GE are provided. The operation of FIG. 3 will be described with reference to FIG. When the one-shot circuit 101 operates after the IGBT 4 is turned on, the transistor 71 of the variable voltage source 70 is turned on. Variable voltage source 70
Has a discharge time constant smaller than that of the variable voltage source 80, and lowers the gate voltage faster than the variable voltage source 80. At the time of a short circuit failure, the gate voltage can be sharply lowered, so that there is an effect that the short circuit current can be reduced as compared with the example of FIG.

At time t = t2 after the timer time of the timer circuit 102, a failure determination is made and another
The transistors 81 of the two variable voltage sources 80 are turned on, and the gate voltage V _GE is further reduced. Variable voltage source 80
Has a large time constant, and lowers the gate voltage V _GE more slowly than the variable voltage source 70. Since the gate voltage V _GE gradually decreases with the lapse of time, the rate of change of the collector current Ic becomes low and the current flowing into the snubber circuit as shown in FIG. 9A becomes small, so that the snubber voltage increases. The advantage is that the IGBT 4 can be turned off more safely than in the example of FIG.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention. The difference from FIG. 1 is that the collector-emitter voltage of the IGBT 4 is divided by the resistors R ₁₀₀ and R ₁₀₁ and drawn into the voltage detection unit 200 of the gate drive circuit of the IGBT 4, and the state of the IGBT 4 is monitored by the detected value. It is in the point that I made it. In this case, the state of the IGBT 4 is monitored by the resistance division value R of the collector-emitter voltage V _CE.
100 / R ₁₀₁ · V _CN (This value is based on the ground line of the gate drive circuit) and the failure set value (V
_{ZD (201)} + V _{BE (203)} ). That is, R ₁₀₀ / R ₁₀₁ · V _CN > V _{ZD (201)} + V _{BE (203)} ... R ₁₀₀ / R ₁₀₁ · V _CN <V _{ZD (201)} + V _{BE (203)} ... When doing, the voltage detection unit 20
The 0 transistor 203 is turned on and outputs a high (H) level signal through the inverting amplifier. When the expression is satisfied, the transistor 203 is turned off and a low (L) level signal is output through the inverting amplifier.

By taking the exclusive OR (EXOR: 104) of the output and the output of the transistor 8, Table 1
It is possible to determine whether or not there is a failure from the relationship. In the failure (1), since the collector-emitter voltage does not drop even though the ON signal is input, the same judgment as in the case of FIG. 1 is made, and the same protection operation as in the case of FIG. 1 is performed. The determination of the failure (2) is as follows. That is, when the IGBT 4 is off, the main circuit voltage is applied to its collector-emitter voltage. On the other hand, if the main circuit voltage does not appear in the collector-emitter voltage of the IGBT 4 even if the OFF signal is given, it is an element failure. Therefore, the state of the IGBT is monitored under this condition, and the information is output to an external control device.

[Table 1]

FIG. 6 is a circuit diagram showing a fourth embodiment of the present invention. This is to receive the state monitoring information of FIG. 5 and, when a failure signal is input, perform a short-circuit protection operation by that signal. Further, when the IGBT element is in the off state, the interlock part 300 is provided which does not receive the on signal and keeps the off state. In this way, by monitoring the states of IGBTs connected in series, the short-circuit protection operation can be performed safely and instantly. Furthermore, when one element is off, when the element on the opposite side has failed, a sound element does not receive the on signal,
The short-circuit state can be prevented by leaving it in the off state.

[0018]

According to the present invention, after the IGBT is turned on, the protection operation for reducing the gate voltage is executed, and after a certain period of time, it is judged whether or not there is a failure. When the failure is judged, the protection operation is continued and the normal operation is performed. If it is determined that the protection operation is stopped and the gate voltage value is returned to the normal value, it is possible to reliably protect the semiconductor element from an overcurrent generated due to a short circuit failure of the voltage-driven semiconductor element. can get.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the operation of FIG.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a waveform diagram for explaining the operation of FIG.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention.

FIG. 6 is a configuration diagram showing a fourth embodiment of the present invention.

FIG. 7 is a waveform diagram for explaining a conventional example.

FIG. 8 is a circuit diagram showing a conventional example.

FIG. 9 is an explanatory diagram of a simulated circuit and its voltage and current waveforms at the time of a short circuit failure.

FIG. 10 is a characteristic diagram showing an output characteristic example of an IGBT.

[Explanation of symbols]

1, 3, 11, 12, 17, 18, 19, 22, 51,
53, 54, 55, 72, 82, 202, 204, R
₁₀₀ , R ₁₀₁ ... Resistance, 2, 13, 50, 201 ... Zener diode, 15, 21 ... Diode, 4, 41, 4
2 ... IGBT, 5 ... Photo coupler, 6, 7 ... Power supply, 8,
9, 10, 14, 23, 52, 71, 81, 203 ... Transistor, 20 ... Capacitor, 24 ... Addition point, 70,
80, 103 ... Variable voltage source, 100 ... Failure detection circuit, 1
01 ... One-shot circuit, 102 ... Timer circuit, 10
4 ... Exclusive OR (EXOR), 200 ... Voltage detection unit,
300 ... Interlock part.

Claims (4)

[Claims] 1. A drive unit having a signal isolator and using a pair of transistors as an output stage, a state monitor unit for monitoring the state of a voltage-driven semiconductor device, and the monitor voltage exceeds a predetermined value. And a determination means for determining an overcurrent failure,
A drive circuit for a voltage-driven semiconductor device comprising an overcurrent protection unit having a variable voltage source that gradually drops the voltage applied to the semiconductor device, wherein the variable voltage source is provided for a certain period after the semiconductor device is turned on. To gradually decrease the voltage applied to the semiconductor element and judge the overcurrent failure.When it is judged as a failure, the voltage applied to the semiconductor element is gradually decreased, but it is judged to be normal. In this case, the drive circuit for the voltage-driven semiconductor element is characterized in that the operation of the variable voltage source is stopped and the voltage applied to the semiconductor element is returned to the normal voltage. 2. A first variable voltage source that operates the variable voltage source only for a certain period after the semiconductor element is turned on, and a second variable voltage source that operates when a failure occurs after an overcurrent failure is determined. 2. The drive circuit for a voltage-driven semiconductor device according to claim 1, wherein the time constants of both variable voltage sources are different from each other. 3. The state monitoring unit is configured to detect the voltage of the semiconductor element by resistance voltage division, and obtain the exclusive OR of the detected value and an input signal to monitor the state of the semiconductor element. The drive circuit for a voltage-driven semiconductor element according to claim 1, 4. The output of the state monitoring unit is mutually input to drive circuits facing each other of a pair of semiconductor elements constituting the power conversion device, and when a failure signal is input, a short circuit protection operation is performed by the signal. 5. The drive circuit for a voltage-driven semiconductor device according to claim 3, wherein when one of the semiconductor devices has a failure, the semiconductor device remains in the off state without receiving the on signal.